Gardai and have ruled out any involvement by mainstream republicans in the murder of British spy Denis Donaldson, it has been learned.

Detectives on both sides of the border knew within hours the murder had been set up and run by a Real IRA leader in Londonderry, supported by sympathisers in Donegal.

Intelligence gathered by the PSNI also ruled out any involvement by the Provisional IRA.

This information was passed to gardai investigating the case who have always focused their attention on dissidents.

The repetition of this position yesterday by security sources raised questions about the claims of the former IRA man and British agent who told the BBC the IRA killed Donaldson. One garda source described it as "a pile of c***".

A reliable security source in Northern Ireland also said there was genuine surprise the BBC Spotlight programme made the allegation.

"No one, and I mean no one, on either side of the border believes this claim has an ounce of truth in it," he added. "The guards say it's nonsense and the PSNI believe the same. The so-called Real IRA did this."